Page:NIOSH Manual of Analytical Methods - 7605.pdf/1

 CHROMIUM, HEXAVALENT by Ion Chromatography Cr(VI)

MW: 52.00 (Cr); 99.99 (CrO3 )

METHOD: 7605, Issue 1

CAS: 18540-29-9

PROPERTIES:

Issue 1: 15 March 2003

oxidizing agent

Vary depending upon the compound; chromate commonly used, “chrome six.”

SAMPLING SAMPLER:

RTECS: GB6262000

EVALUATION: FULL

OSHA : 0.1 mg/m3 (as CrO3 ) NIOSH: 0.001 mg/m3 /10 h; carcinogen ACGIH: 0.050 mg/m3 (as Cr, soluble); some insoluble chromates are human carcinogens

SYNONYMS:

7605

FILTER (5.0-:m PVC membrane)

FLOW RATE: 1 to 4 L/min

MEASUREMENT TECHNIQUE:

Ion chromatography with post-column derivatization and UV detection.

ANALYTE:

CrO4 -2 -diphenylcarbazide (DPC) complex 5 mL 2% NaOH- 3% Na2 CO3. Dilute to 25 mL after heating.

VOL-MIN: -MAX:

1 L @ 0.05 mg/m3 400 L

EXTRACTION:

SHIPMENT:

Routine. Can be shipped cold when deemed necessary.

INJECTION VOLUME:

100 :L

COLUMN:

Dionex NG1 Guard, HPIC- AS7 Separator or equivalent

MOBILE PHASE:

250 mM (NH4 )2 SO4 /100 mM NH4 OH

FLOW RATE:

1.0 mL/min; 0.7 mL/min post column

POST-COLUMN REAGENT:

2.0 mM DPC + 10% MeOH +1N H2 SO4

DETECTOR:

540 nm

CALIBRATION:

Standard solutions of K2 Cr2 O7 in NaOH-Na2 CO3 buffer

OVERALL PRECISION (Ö r T ): 0.07

RANGE:

0.05 to 20 :g per sample

ACCURACY:

ESTIMATED LOD: 0.02 :g per sample [3]

SAMPLE STABILITY:

BLANKS:

Stable for 2 weeks at room temperature. Stable for 4 weeks if stored in refrigerator. 2 to 10 field blanks per set

ACCURACY RANGE STUDIED:

0.05 to 120 :g Cr(VI) [1,2]

BIAS:

-1.6% [2]

± 17.4% (0.6 - 960 :g/m3 ) [1]

PRECISION ( þ r ):

0.015 @ 0.5 to 5 :g/sample [3]

APPLICABILITY: The working range is 0.00025 to 0.1 mg/m3 for a 200-L air sample. This method can be used for the determination of Cr(VI) using 2% NaOH - 3% Na2 CO3 for extraction. INTERFERENCES: Possible interferences are iron, copper, nickel, and vanadium; 10 :g of any of these causes an absorbance equivalent to approximately 0.02 :g Cr(VI) due to formation of colored complexes. Interference due to reducing agents (e.g., Fe, Fe++) is minimized by alkaline extraction (step 5). OTHER METHODS: Method 7703 is a field portable method for Cr(VI). OSHA Method W4001 is for the measurement of Cr(VI) in wipe samples [4]. OSHA Method ID-215 is for measurement of Cr(VI) and employs precipitation to reduce Cr(III) oxidation. [5]. A similar air method is ISO 16740 [6]. EPA Method 218.6 is for water matrices [7]. Method 7604 is also specific for hexavalent chromium, using ion chromatography, but has a higher detection limit than 7605.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition